rgb overlay now correctly handles alpha

Author: itzpr3d4t0r

src_c/simd_blitters_avx2.c

@@ -743,26 +743,35 @@ blit_blend_rgb_overlay_avx2(SDL_BlitInfo *info)
 
     const __m256i mm256_255 = _mm256_set1_epi16(255);
     const __m256i mm256_127 = _mm256_set1_epi16(127);
+    const __m256i mm256_amask = _mm256_set1_epi32(info->dst->Amask);
+    const __m256i mm256_rgb_mask = _mm256_set1_epi32(~info->dst->Amask);
 
-    RUN_AVX2_BLITTER(RUN_16BIT_SHUFFLE_OUT(
-        /* src * dst */
-        __m256i multiply = _mm256_mullo_epi16(shuff_src, shuff_dst);
-        /* divide by 127 */
-        multiply = _mm256_srli_epi16(multiply, 7);
-
-        /* 255 - dst */
-        __m256i inverted_dst = _mm256_subs_epu16(mm256_255, shuff_dst);
-        /* 255 - src */
-        __m256i inverted_src = _mm256_subs_epu16(mm256_255, shuff_src);
-        /* dst * src */
-        __m256i screen = _mm256_mullo_epi16(inverted_dst, inverted_src);
-        /* divide by 127 */
-        screen = _mm256_srli_epi16(screen, 7);
-        /* 255 - screen */
-        screen = _mm256_subs_epu16(mm256_255, screen);
-
-        __m256i gt_127 = _mm256_cmpgt_epi16(shuff_dst, mm256_127);
-        shuff_dst = _mm256_blendv_epi8(multiply, screen, gt_127);))
+    __m256i mm256_dst_alpha;
+
+    RUN_AVX2_BLITTER(
+        mm256_dst_alpha = _mm256_and_si256(pixels_dst, mm256_amask);
+        RUN_16BIT_SHUFFLE_OUT(
+            /* src * dst */
+            __m256i multiply = _mm256_mullo_epi16(shuff_src, shuff_dst);
+            /* divide by 127 */
+            multiply = _mm256_srli_epi16(multiply, 7);
+
+            /* 255 - dst */
+            __m256i inverted_dst = _mm256_sub_epi16(mm256_255, shuff_dst);
+            /* 255 - src */
+            __m256i inverted_src = _mm256_sub_epi16(mm256_255, shuff_src);
+            /* dst * src */
+            __m256i screen = _mm256_mullo_epi16(inverted_dst, inverted_src);
+            /* divide by 127 */
+            screen = _mm256_srli_epi16(screen, 7);
+            /* 255 - screen */
+            screen = _mm256_sub_epi16(mm256_255, screen);
+
+            __m256i gt_127 = _mm256_cmpgt_epi16(shuff_dst, mm256_127);
+            shuff_dst = _mm256_blendv_epi8(multiply, screen, gt_127);
+
+            ) pixels_dst = _mm256_and_si256(pixels_dst, mm256_rgb_mask);
+        pixels_dst = _mm256_or_si256(pixels_dst, mm256_dst_alpha);)
 }
 #else
 void